Mettle

[Sarah]

Substance or quality of temperament; spirit, esp. as regardshonor, courage, fortitude, ardor, etc.; disposition; -- usually in agood sense.A certain critical hour which shall... try what mettle his heart ismade of. South.Gentlemen of brave mettle. Shak.The winged courser, like a generous horse, Shows most true mettlewhen you check his course. Pope.To put one one's mettle, to cause or incite one to use one's bestefforts.

[Sarah]

the ability or driving force of an individual to [persevere] when they think they can't go any farther.

[Sarah]

Ability to persevere despite obstacles...usually performed with class or grace.